1. Field of the Invention
The present invention relates to a corneal surgery apparatus which ablates a cornea by irradiation of a laser beam.
2. Description of Related Art
Conventionally, there is known a corneal surgery apparatus which ablates a cornea by irradiation of a laser beam and changes a shape of a corneal surface to correct a refractive error of an eye. In many apparatuses of this kind, a patient (a patient's eye) is made fixate on a fixation lamp during a surgery, and a pupil center position of the eye at that time is taken as a reference when alignment of an irradiation position of the laser beam is performed. However, in the case of the patient who is not good at fixation, an eyeball sometimes moves, which leads to difficulty in maintaining accurate alignment. Thus, there is proposed a corneal surgery apparatus which detects the pupil center position based on a picked up image of an anterior-segment of the eye to perform alignment, and in a case where the pupil center position is moved, moves (performs tracking of) the irradiation position in accordance with the movement of the pupil center position to maintain the alignment.
However, in the method of moving the irradiation position with reference to the pupil center position, if there occurs duction in the eye (monocular eyeball movement such as supraduction, infraduction, adduction and abduction), the irradiation position on the cornea is displaced (deviated) due to a height difference between the pupil and the corneal surface. That is to say, as shown in FIG. 4, a position P is a position on the cornea corresponding to the pupil center position EPc detected in the image-pickup direction (Z direction) when the eye is horizontally positioned (is in a reference state), while a position Pd is a position on the cornea corresponding to the pupil center position EPc detected in the image-pickup direction when the duction occurs, which is displaced (deviated) by an amount of ΔL. In order to perform accurate keratorefractive surgery, it is desired that the laser beam be irradiated with reference to a given position on the cornea.